1. Field of the Invention
The present invention relates to an electro-luminescent display (ELD) and a method of manufacturing thereof. More specifically, the present invention relates to an active ELD including an organic luminescent layer.
2. Discussion of the Related Art
An ELD is a luminescent device that emits light when electrons and holes that are injected into a luminescent layer recombine. The emission of light by the recombination of electrons and holes eliminates the need for a back-light in the ELD. Thus, it is easy to manufacture a very thin panel using an ELD. Further, the ELD has the added advantage of low power consumption. Additionally, an organic ELD, having a light-emitting layer with an organic electro-luminescent (EL) substance, is characterized by a low driving voltage, high light-emitting efficiency, and low process temperature. However, organic EL substances are vulnerable to moisture so that the patterns are defined by a method that prevents the organic EL substance from contacting moisture directly, unlike conventional photolithography.
In an active ELD, a plurality of pixel cells are defined by providing a plurality of scanning lines that cross with a plurality of signal lines, and also such that a power supply line is arranged in the same direction as the signal line in each of the pixel cells. Each pixel cell includes a storage capacitor, an EL portion, and at least one switching device such as a thin film transistor (TFT).
When the pixel cell includes two TFTs, an excitation signal for the EL portion is distinguished from the scanning signal. The EL portion is selected by a logic TFT which is the first TFT, and the excitation signal for the EL portion is controlled by the second TFT. The storage capacitor then maintains the excitation power in the EL portion of the selected cell.
FIG. 1A to FIG. 1D illustrate a method of manufacturing an ELD according to a related art method. Referring to FIG. 1A, polysilicon is deposited on an insulating substrate 11 having a switching part and a pixel part, via a chemical vapor deposition (CVD) process. Then an active layer 13 is formed by patterning the polysilicon via a photolithography process. An insulating substance such as silicon oxide, silicon nitride, or other similar substances are then deposited on the insulating substrate 11 to cover the active layer 13. Next, an electrically-conductive substance is deposited on the insulating substance. Then, a gate insulating layer 15 and a gate electrode 17 is formed by sequentially patterning the electrically-conductive substance and the insulating substance so that they remain on the middle portion of the active layer 13. Note that a scanning line (not shown in the drawing) that is connected to the gate electrode 17 may be provided as soon as the gate electrode 17 is formed. A source region 19 and a drain region 21 are then formed by heavily doping the exposed portions of the active layer 13 with either n type or p type impurities with the gate electrode 17 functioning as a mask. Note that the middle portion of the active layer 13, which is not doped with impurities, becomes a channel region.
Referring to FIG. 1B, a first insulating interlayer 23 is then provided and covers the active layer 13, the gate electrode 17, and the scanning line by depositing an insulating substance such as silicon oxide, silicon nitride, or other similar substances on the insulating substrate 11. Next, the first insulating interlayer 23 is patterned to expose the source region 19 and the drain region 21, and a source electrode 25 and a drain electrode 27 are connected electrically with the exposed source region 19 and exposed drain region 21, respectively, by depositing and then patterning a known conductive substance. Thus, a TFT that functions as a switching device is manufactured. Note that a signal line (not shown in the drawing) may be defined on the insulating interlayer 23 at the same time the source electrode 25 and the drain electrode 27 are provided.
Referring to FIG. 1C, a second insulating interlayer 29 is provided and covers the source electrode 25 and the drain electrode 27 and the signal line by depositing silicon oxide or silicon nitride on the first insulating interlayer 23. A contact hole 30 exposes the drain electrode 27 and is provided by patterning the second insulating interlayer 29. Next, a transparent conductive substance is deposited so as to contact the exposed portion of the drain electrode 27 through the contact hole 30 that is provided in the second insulating interlayer 29. Then, an anode electrode 31 is formed by patterning via a photolithography process the transparent conductive substance so that the anode electrode 31 remains in the pixel portion of the second insulating interlayer 29. Note that the anode electrode 31 is electrically connected to the drain electrode 27, and is isolated electrically from other anode electrodes in adjacent pixel cells.
Referring to FIG. 1D, a passivation layer 33 covers the anode electrode 31 by the deposition of silicon oxide or silicon nitride on the second insulating interlayer 29. Alternatively, the passivation layer 33 may be formed with an organic substance such as BCB (benzocyclobutene), SOG(spin-on glass), and other similar substances. Note that the passivation layer 33 made of an organic substance may be relatively thick in order to provide an even surface. Next, the passivation layer 33 is patterned via a photolithography process, including a dry etching process, so as to expose the anode electrode 31. An organic EL layer 35, which emits a predetermined color such as red, blue, or green, is provided on the passivation layer 33 by an evaporation process. Note that the organic EL layer 35 just contacts the anode electrode 31 and the exposed pixel portion. Next, a cathode electrode 37, which functions as a common electrode and is connected to ground, is disposed on the organic EL layer 35.
As mentioned in the above description, the ELD of the related art carries out the switching operation by selecting a TFT that has an n-type channel in a certain pixel, which has a predetermined signal line (not shown in the drawing) crossing with a predetermined scanning line (not shown in the drawing), such that a ‘high’ signal is applied to the predetermined scanning line while a ‘high’ signal is applied to the predetermined signal line. Thus, the selected TFT turns on and transfers the signal of the predetermined signal line to the drain electrode by which holes are injected into the organic EL layer via the anode electrode and electrons are injected into the organic EL layer via the grounded cathode electrode. Thus, the pixel cell achieves light-emission through the recombination of electrons and holes.
Unfortunately, in the structure and method of the related art, the exposed portion of the anode electrode is easily damaged by the collision of the ions when dry-etching the passivation layer for exposing the anode electrode. Further, contaminant particles, albeit a small amount, remain on the exposed portion of the anode electrode after the etching process. Thus, the damage to the anode electrode caused by the collision of the ions during the etching process and the remaining contaminant particles on the anode electrode after the etching process creates a barrier interface between the anode electrode and the EL layer that hinders the efficient transport of charge carriers such as holes. Therefore, the expected life span, brightness, and efficiency of the ELD suffers greatly from the structure and method of the related art.